When you are using any color (or image) as background in the world settings you have to imagine a shpere that completely surrounds the scene and that is emitting colored light from every point.

There are a few alternatives.

• One is to have two different shaders for the background, and control them using a light path node, so that difuse rays are a neutral color and the rest are green.

• You can use a neutral color (or no background at all) for the background and enable transparency (film transparent), and then add the background color in the compositor using alpha over.

When you are using any color (or image) as background in the world settings you have to imagine a shpere that completely surrounds the scene and that is emitting colored light from every point.

There are a few alternatives.

• One is to have two different shaders for the background, and control them using a light path node, so that difuse rays are a neutral color and the rest are green.

• You can use a neutral color (or no background at all) for the background and enable transparency (film transparent), and then add the background color in the compositor using alpha over.

I hope you are not putting green behind the object with the idea of using a chroma key later on to take away the background. If that is the case then just render with a transparent background and save in a format that can handle an alpha channel (EXR or TIFF).